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Independent Study: LRH calibres - 7mm WSM vs 300 RUM vs 338 LM

 
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Old 03-24-2012, 07:59 PM
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Independent Study: LRH calibres - 7mm WSM vs 300 RUM vs 338 LM

Hello,

A friend recently lent me a book I'm sure (and hope) many of you are familiar with. The book is 'Applied Ballistics for Long Range Shooting' by Bryan Litz from Berger Bullets. Wow, what an amazing book, definately going to buy one for myself! His style of writing really appeals to the aeronautical engineer in me. I don't even like reading books but this one is a real page turner; and here I was going into it thinking I knew it all. I was wrong.


Anyway, reading his chapters on bullet lethality and long range hit probability got me goin' on the spreadsheets. Matunas' Optimal Game Weight equation started making me criticize my earlier decision to use a 7mm WSM for a future long range hunting rig. From everything I had read previous to this book, the only good answer I could get for bullet lethality was '1000 ft pounds of force'. Maybe for a female deer but not for serious game as it turns out.



To start putting things into perspective, I plotted a graph of velocity vs OGW for a given calibre/bullet weight and then used the ballistics calculator to match a range to the required velocity to take out a large 1000lb Roosevelt Elk and a 450lb Mule Deer. I picked the 7mm WSM, 300 RUM, and 338 LM because they seem to be some of the most popular precise, non-belted, non-wildcat, 'moderate' barrel burning heavy hitters, all with comparable ballistics.


What I found was rather interesting and honestly, a little disappointing. The 7mm WSM isn't as powerful as I thought; however, it should still be able to take out an oversized Elk at short range (ideally, however, not with a fragile Berger), so not all hope was lost. I also stumbled upon a thread here on LRH spreading the rumor about the new Berger 7mm 195gn bullet. But I digress.



For this study, I used the heaviest, most aerodynamic bullets on the market, all from Berger. I used typical muzzle velocities for a 30" barrel and slow powder. If you can update my numbers based on your real life MVs, I'd be greatful!


















As you can see, the OGW method indicates that a heavier calibre requires less energy to take down an animal than the smaller calibre. Can anyone help me explain that one? I guess a larger hole means more hydrostatic shock or something...



After reading about the new 195gn 7mm bullet, I couldn't resist and modified the graph to include this new development. I used one of Bryan's formulas to calculate the new MV for the heavier bullet based on constant pressure. (M1V1^2 = M2V2^2)



As you can see, there is not much of a benefit between the two bullet weights at short ranges on heavy animals. There's only a 20 yard benefit for the big 195gn on large elk. However, at extended ranges on smaller animals, this new bullet should give us an additional 125 yards of effective range on a large deer. Its not hard to assume this based on the higher BC and better retention of velocity, but I thought I'd make that conclusion while I was at it.




Look forward to hearing your thoughts!
Kevin
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Last edited by Haagen Dazs; 03-24-2012 at 08:32 PM.
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Old 03-24-2012, 08:48 PM
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Re: Independent Study: LRH calibres - 7mm WSM vs 300 RUM vs 338 LM

Dont have the book but of course know of his work. I always watched the energy on bullets at range. That is why over 20 yrs. ago I hung up my 7mm, for a 340wby.Which my son uses.I shoot the lapua's little brother, 338 Norma w/300 pill,getter done
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Old 03-25-2012, 10:33 AM
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Re: Independent Study: LRH calibres - 7mm WSM vs 300 RUM vs 338 LM

Very nice work. I see you used 3200 fps as a velocity ceiling. Smart. I've hered conflicting reports on shoving Bergers any harder/faster.
I'm a 30 cal freak, especially for an allround rifle, near to far, gopher to griz, but I will readily admit that the 338 is in a different class, especially for LR work.
Your graph shows what many have preached for years. Bigger is better period in the energy department when comparing optimal to optimal BC's. It's pretty clear where each round gives up to the next.
Many folks here may choose to disagree with it, & I'm sure they'll chime in sooner or later. Be interesting to see what they say.

As a side note, will a 7WSM even shove a bullet that heavy to 3200fps? Not that it matters, cause all the bullets on the graph started at the same 3200fps, thus rendering all the cartriges dead even at the starting line.

This should make for an excellent discussion. Great thread starter.
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Last edited by winmag; 03-25-2012 at 12:37 PM. Reason: had a question to add into my post
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Old 03-25-2012, 11:42 AM
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Re: Independent Study: LRH calibres - 7mm WSM vs 300 RUM vs 338 LM

Im sure he will chime in on this discussion
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Old 03-25-2012, 12:29 PM
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Re: Independent Study: LRH calibres - 7mm WSM vs 300 RUM vs 338 LM

Hmm. I'm looking forward to Brians book myself. That said, I don't buy your numbers. Perhaps "optimal" performance may be achieved at your ranges, whatever that means.

I've killed a small pile of elk with the 180's from 750 to 1200 yards. Maybe they aren't "optimally" dead, I'll ask. Personally, I'd put a 180 in a bulls chest to 1500 yards where I live and hunt.

How do handguns fit into your numbers? Is a 44 mag only fit for three pound jack rabbits at ten yards? How about my bow? Will it bounce of at inches?

I like your idea. It's fun, and food for thought, fur sure.
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Old 03-25-2012, 01:00 PM
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Re: Independent Study: LRH calibres - 7mm WSM vs 300 RUM vs 338 LM

Maybe you could make a graph using 1500# for Elk, & 1000# for Deer, since they're "more readily accepted" by most members here. Not that I nesicarily disagree with your current #'s, but obviously some folks will/do.
It may close the gap on the graph & extend the range a bit, but I'd guess the outcome would be the same. 338 on top, 7 on the bottom, & 300 splitting the two.

Grit, what elevation, muzzle velocity, & bullet are you using to get 1500# at 1500yds? Just curious, as I have not personally done the math yet. (oh, & I enjoyed visiting your website. Very nicely done, & easy to navigate).
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Old 03-25-2012, 01:59 PM
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Re: Independent Study: LRH calibres - 7mm WSM vs 300 RUM vs 338 LM

From a retired US Navy Officer and SEAL close to sniper rifle and marksmanship issues:

When the Precision Sniper Rifle (PSR) program compared the AI 338 LM/300 gr Lapua with the Long throat 300 WM/190 & 220 MK (Army, Navy and Marine snipers, including a couple of Palma shooters ) the 300 WM outperformed the 338 Lapua at 1000, 1200, and 1500 yards. The Long throat 300 WM/ 190 MK @ 3100 FPS was the most accurate at 1000 and 1200 yards. The 300 WM/ 220 MK was the most accurate load at 1500 yards, however none of the participants could meet the one MOA PSR requirement. The shooters were unable to keep five shots on the 6'X6' targets in a 5-20 knot gusting wind except with the 300 WM. The Army has continued to pursue the AI 338 LM because it purports to do the job of the 300 WM and the 50 SASR...it does neither job as well.
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